In an electromagnetic relay, a sudden external disturbance such as an external shock sometimes causes an electrical connection in the relay to become off. For example, an external disturbance detaches a plate (, or an armature) from a coil of the relay and accordingly turns the relay to OFF.
In JP 2005-50733A, an art is proposed which regains the ON state of the relay by supplying electric power to the coil on detecting that the relay is turned to OFF.
However, since the conventional art regains the ON state after the relay gets to the OFF state, the conventional art cannot prevent it from occurring that the relay is temporality turned to OFF and power supply from the relay to a load is accordingly cut off.
In view of this, another conventional art supplies the coil with a holding current which has such excessive a current value that the external disturbance cannot detach the plate from the coil. With this conventional art, the relay is not turned to OFF because of some external disturbance resulting from certain usages of the relay and steady external disturbances resulting from degradation of the relay.
In this conventional art, the relay consumes much power because it is supplied with the holding current acting as a measure against the external disturbance even if the external disturbance is not occurring. In addition, the relay and a relay drive circuit produce much heat, which may harm a primary purpose of the relay and the relay drive circuit to reduce an amount of heat produced by the relay and the relay drive.